Can I upload parts of tv shows onto youtube?

Technically, no. Practically, yes.

(And if you’re the one the copyright cartel chooses to make an example of, don’t come crying to me.)

You have limited rights under Fair Use doctrine, but if it is under 30 seconds and falls into the category of “criticism, comment, news reporting, teaching, scholarship, [or] research” then you are legally protected. Kind of.

More info at http://www.copyright.gov/fls/fl102.html.

Frankly, though, it’s not worth the trouble unless you have legitimate uses in mind.